In recent years, as RF communication technology has progressed, various applications of near field communication (NFC) have been developed. For example, in a surface computer 10 as illustrated in FIG. 1, an RF device 11 such as a mobile phone or a radio frequency identification (RFID) tag is placed on a display panel 12. In this way, the RF device 11 can communicate with a host computer 14 through an RF module 13, which includes an antenna and an associated RF circuit and is located at the back side of the display panel 12. For example, the RF device 11 first sends pictures stored therein to the host computer 14, and after having been processed and transmitted by the host computer 14, the pictures are displayed near the RF device 11 at the display panel 12 for a user to view.
However, when the RF device 11 communicates with the host computer 14, especially when a large amount of information is transmitted, power of the RF device 11 is consumed rapidly. Therefore, the surface computer 10 needs an RF charging capability in order to charge the RF device 11 and prevent the power depletion of the RF device 11.